Light emitting device and illumination device

ABSTRACT

According to one embodiment, a light emitting device includes a light guide plate with a plurality of first protrusion parts arranged along a first direction and extending along a second direction which crosses the first direction, and a prism sheet, wherein a cross-sectional shape of each of the first protrusion parts along the first direction has an apex angle between 55 degrees and 65 degrees, inclusive, the light guide plate includes a plurality of second protrusion parts which extend along the first direction and are arranged along the second direction, and a cross-sectional shape of each of the second protrusion parts along the second direction has a base angle between 1 degree and 3 degrees, inclusive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/220,503, filed on Apr. 1, 2021. Further, this application is basedupon and claims the benefit of priority from Japanese Patent ApplicationNo. 2020-067778, filed, Apr. 3 2020, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a light emitting deviceand an illumination device.

BACKGROUND

Light emitting devices with a planar light emission function have beendeveloped.

A light emitting device which includes a light source disposed in a sidesurface of a light guide plate such that light is emitted from a mainsurface disposed at a certain angle with respect to the side surface isused as a surface light source. For example, such a light emittingdevice is used as a backlight of a liquid crystal display device.

In order to suppress a change in luminosity by an observation angle of aliquid crystal display device, the light emitting device for thebacklight of the display device is required to have a wider lightemission angle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the structure of a display device ofan embodiment.

FIG. 2A is a perspective view of the structure of a light emittingdevice in a disassembled manner.

FIG. 2B is a perspective view of the structure of the light emittingdevice in a disassembled manner.

FIG. 2C is a perspective view of the structure of the light emittingdevice in a disassembled manner.

FIG. 3A illustrates a cross-sectional shape of a light guide plate.

FIG. 3B illustrates a cross-sectional shape of the light guide plate.

FIG. 4A illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 4B illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 5A illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 5B illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 6A illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 6B illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 7A illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 7B illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 8A illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 8B illustrates emission angle distribution characteristics withrespect to an apex angle θ1.

FIG. 9 illustrates a relationship between the apex angle θ1 and anemission angle φh.

FIG. 10 illustrates a relationship between the apex angle θ1 and a noiserelative value.

FIG. 11A illustrates a change in emission angle φv of emission light Lbased on the base angle θ2.

FIG. 11B illustrates a change in emission angle φv of emission light Lbased on the base angle θ2.

FIG. 11C illustrates a change in emission angle φv of emission light Lbased on the base angle θ2.

FIG. 12A illustrates emission angle distribution characteristics withrespect to an apex angle θ2.

FIG. 12B illustrates emission angle distribution characteristics withrespect to an apex angle θ2.

FIG. 13A illustrates emission angle distribution characteristics withrespect to an apex angle θ2.

FIG. 13B illustrates emission angle distribution characteristics withrespect to an apex angle θ2.

FIG. 14 illustrates a relationship between the base angle θ2 and anemission angle φv.

FIG. 15 illustrates an example of the structure of an illuminationdevice.

FIG. 16 is a schematic cross-sectional view of a light collectiondevice.

FIG. 17 is a plan view illustrating a shape of an electrode of the lightcollection device.

FIG. 18A illustrates a light emitting device of an example.

FIG. 18B illustrates the light emitting device of the example.

DETAILED DESCRIPTION

In general, according to one embodiment, a light emitting deviceincludes: a light guide plate with a first main surface on which aplurality of first protrusion parts arranged along a first direction andextending along a second direction which crosses the first direction; aplurality of light source elements disposed on a side surface of thelight guide plate to be adjacent to each other; and a prism sheetdisposed to be opposed to the first main surface, wherein an emissionsurface of the light source element is disposed in the second direction,and a cross-sectional shape of each of the first protrusion parts alongthe first direction has an apex angle between 55 degrees (55°) and 65degrees (65°), inclusive (in a range of larger than and equal to 55degrees (55°), and smaller than and equal to 65 degrees (65°)), and thelight guide plate includes a plurality of second protrusion parts on asecond main surface, which extend along the first direction and arearranged along the second direction, and a cross-sectional shape of eachof the second protrusion parts along the second direction has a baseangle between 1 degree (1°) and 3 degrees (3°), inclusive.

According to an embodiment, a light emitting device which can emitcollimated light can be presented.

Embodiments will be described hereinafter with reference to theaccompanying drawings. The disclosure is merely an example, and properchanges within the spirit of the invention, which are easily conceivableby a skilled person, are included in the scope of the invention. In somecases, in order to make the description clearer, the widths,thicknesses, shapes, etc., of the respective parts are schematicallyillustrated in the drawings, compared to the actual modes. However, theschematic illustration is merely an example, and adds no restrictions tothe interpretation of the invention. In the specification and drawings,the same elements as those described in connection with precedingdrawings are denoted by like reference numerals, and a detaileddescription thereof may be omitted.

Hereinafter, an light emitting device of an embodiment will be explainedwith reference to the accompanying drawings.

In the embodiment, a first direction X, second direction Y, and thirddirection Z cross each other. The first direction X, second direction Y,and third direction Z may be orthogonal to each other, or may cross eachother at an angle other than 90 degrees (90°). A direction toward thetip of arrow of the third direction Z will be defined as up or above,and a direction opposite to the direction toward the tip of arrow of thethird direction Z will be defined as low or below.

Furthermore, phrases such as “a second member above a first member” and“a second member below a first member” may be interpreted as the secondmember contacting the first member or as the second member apart fromthe first member. In the latter case, a third member may be interposedbetween the first member and the second member. On the other hand,phrases such as “a second member on a first member” and “a second memberunder a first member” will be interpreted as the second membercontacting the first member.

Furthermore, a hypothetic observation position to observe a displaydevice DSP is set in the tip side of arrow of the third direction Z, andseeing an X-Y plan view defined by the first direction X and the seconddirection Y from this observation position will be referred to as planview. Seeing a cross-sectional view of the display device DSP along anX-Z plan view defined by the first direction X and the third directionZ, or along a Y-Z plan view defined by the second direction Y and thethird direction Z will be referred to as cross-sectional view.

Embodiment

FIG. 1 is a cross-sectional view of the structure of the display deviceof the embodiment. A light emitting device ILD of FIG. 1 includes, alongthe third direction Z, a reflection sheet REF, light guide plate LG, andprism sheet PRM. Furthermore, the light emitting device ILD includes alight source element LS1 disposed to be adjacent to a side surface LG1 sof the light guide plate LG.

The light guide plate LG includes a first main surface LGa (or mainsurface LGa) opposed to the prism sheet PRM and a second main surfaceLGb (main surface LGb) opposed to the reflection sheet REF. The mainsurface LGa is positioned above the main surface LGb, and is an emissionsurface of the light guide plate. Furthermore, the main surface LGb isopposed to the main surface LGa and is disposed in the opposite sidethereof. On the main surface LGa and the main surface LGb, triangularprism shaped first protrusion parts and second protrusion parts aredisposed. The protrusions parts will be explained later.

In the example of FIG. 1 , a light source element LS1 is disposed to beadjacent to a first side surface LG1 s of the light guide plate LG, anda light source element LS2 is disposed to be adjacent to a second sidesurface LG2 s opposite to the first side surface LG1 s. Note that, inFIG. 1 , one light source element LS1 and one light source element LS2are shown; however, there may be multiple light source elements LS1 andmultiple light source elements LS2. Furthermore, instead of the lightsource elements LS1 and LS2, light source elements LS1 alone or lightsource elements LS2 alone may be disposed.

Furthermore, in the present embodiment, if there is no need ofdistinguishing the light source element LS1 from the light sourceelement LS2, they may be referred to as a light source element LS.Furthermore, if there is no need of distinguishing the first sidesurface LG1 s from the second side surface LG2 s, they may be referredto as a side surface.

Light emitted from the light source element LS1 is, along the seconddirection Y, incident on the light guide plate LG through the sidesurface LG1 s of the light guide plate LG. The light emitted from thelight source element LS2 is, along the opposite direction of the seconddirection Y, incident on the light guide plate LG through the sidesurface LG2 s of the light guide plate LG. The side surface LG1 s of thelight guide plate LG is a light incident surface, and the side surfaceG2 s is a light incident surface of the light source element LS1. Thesurface of the light source element LS1 which is opposed to the sidesurface LG1 s of the light guide plate LG in the second direction Y isan emission surface of the light source element LS1. Furthermore, thesurface of the light source element LS2 which is opposed to the sidesurface LG2 s of the light guide plate LG in the second direction Y isan emission surface of the light source element LS2. The light incidenton the light guide plate LG propagates in the light guide plate LG to beemitted above. At that time, the light emitted from the light guideplate LG is incident on the prism sheet PRM with multiple inclinedangles. The light incident on the prism sheet PRM is emitted by theprism sheet PRM in a direction parallel to the third direction Z. Asdescribed above, the light emitting device ILD can emits collimatedlight in which light beams are all parallel to the third direction Z.

FIGS. 2A, 2B, and 2C illustrate the structure of the light emittingdevice. FIG. 2A is a perspective view of the structure of the lightemitting device in a disassembled manner. As in FIG. 2A, the light guideplate LG includes a plurality of triangular prism shaped firstprotrusion parts TRVa (protrusion parts (convex portions) TRa) on thefirst main surface LGa. Each of the protrusion parts TRVa extend alongthe second direction Y. The protrusion parts TRVa are arranged along thefirst direction X which crosses the second direction Y. Thecross-sectional shape of one protrusion part TRVa in the first directionX is an isosceles triangle, and the cross-sectional shape in the seconddirection Y is a rectangle. Specifically, the apex of the isoscelestriangle is positioned above the base.

Furthermore, the light guide plate LG includes, on the second mainsurface LGb, a plurality of triangular prism shaped second protrusionparts TRVb (protrusion parts (convex portions) TRb). Each protrusionpart TRVb extends along the first direction X. The protrusion parts TRVbare arranged along the second direction Y. The cross-sectional shape ofone protrusion part TRVb in the second direction Y is an isoscelestriangle, and the cross-sectional shape in the first direction X is arectangle. Specifically, the apex of the isosceles triangle ispositioned below the base.

Note that the direction in which the protrusion part TRVa extends(second direction Y) and the direction in which the protrusion part TRVbextends (first direction X) cross at an angle other than 90 degrees;however, they should be orthogonal to each other.

The light guide plate LG is, for example, formed of a transmissive resinmaterial. The protrusion parts TRVa and TRVb are formed integrally withthe light guide plate LG using, for example, a transmissive resinmaterial. In other words, the main surface LGa of the light guide plateLG has a prism shape including a plurality of protrusion parts TRVa, andthe main surface LGb of the light guide plate LG has a prism shapeincluding a plurality of protrusion parts TRVb.

One protrusion part TRVa includes a ridge RDGa. Between ridges RDGa,valleys (valley portions) VLYa are disposed. The direction in which theridge RDGa and the valley VLYa extend is the direction in which theprotrusion part TRVa extends (second direction Y).

One protrusion part TRVb includes a ridge RDGb. Between ridges RDGb,valleys VLYb are disposed. The direction in which the ridge RDGb and thevalley VLYb is the direction in which the protrusion TRVb extends (firstdirection X).

In other words, the light guide plate LG includes the main surface LGawith a plurality of protrusion parts TRVa with ridges RDGa extending inthe second direction Y, and includes valleys VLYa between adjacentridges RDGa. An inclined surface is arranged from the ridge RDa to thevalley VLYa. The ridge RDGa, valley VLYa, and inclined surface shape anisosceles triangle in the first direction X.

Furthermore, the light guide plate LG includes the main surface LGb witha plurality of protrusion parts TRVb with ridges RDGb extending in thefirst direction X, and includes valleys VLYb between adjacent ridgesRDGb. An inclined surface is arranged from the ridge RDb to the valleyVLYb. The ridge RDGb, valley VLYb, and inclined surface shape anisosceles triangle in the second direction Y.

The prism sheet PRM is disposed above the light guide plate LG to beopposed to the light guide plate LG. The prism sheet PRM includes a mainsurface PRMb (third main surface) opposed to the light guide plate LG,and a main surface PRMa (fourth main surface) positioned in the oppositeside of the main surface PRMb to emit light.

On the main surface PRMb, a plurality of triangular prism shaped thirdprotrusion parts TRVp (protrusion parts (convex portions) TRVp)extending along the first direction X and arranged along the seconddirection Y. The cross-sectional shape of one protraction part TRVp inthe second direction Y is an isosceles triangle, and the cross-sectionalshape in the first direction X is a rectangle. Specifically, the apex ofthe isosceles triangle is positioned below the base of the isoscelestriangle. The prism sheet PRM is a so-called reverse prism sheet.

The reflection sheet REF of FIG. 2A has a function to reflect the lightleaked from the main surface LGb of the light guide plate LG to bereturned in the light guide plate LG. Thus, light extraction efficiencycan be improved. The reflection sheet REF has a mirror surface in thesurface opposed to the light guide plate LG, and is formed of a sheet towhich a metal such as silver is deposited, for example. Note that, thereflection sheet REF is not limited to a metal-deposited sheet, and maybe a metal thin-films layered sheet, optical absorption sheet, or blacksheet, for example.

FIGS. 2B and 2C illustrate an emission angle of emission light L. As inFIG. 2B, a hypothetical sphere is set in a space on the light guideplate LG in a latitudinal (horizontal) direction of the light guideplate LG (horizontal) and a longitudinal (vertical) direction of thelight guide plate LG. In FIGS. 2B and 2C, an angle formed by theemission light L emitted from the light emitting device ILD and thethird direction Z in the Y-Z plan is an emission angle φv. Similarly, anangle formed by the emission light L and the third direction X in theX-Z plan is an emission angle φh. The emission angle φv is between −90degrees and 90 degrees, inclusive (−90 degrees≤φv≤90 degrees) (in rangeof larger than and equal to −90 degrees, and smaller than and equal to90 degrees), and the emission angle φh is between −90 degrees and 90degrees, inclusive (−90 degrees≤φh≤90 degrees) (in range of larger thanand equal to −90 degrees, and smaller than and equal to 90 degrees. Theideal collimated light should satisfy φv=φh=0 degrees; however, theactual emission light L has an emission angle range, which will bedescribed later.

FIGS. 3A and 3B illustrate cross-sectional shapes of the light guideplate LG. FIG. 3A is a cross-sectional view of the light guide plate LG,taken along line A1-A2 of FIG. 2A. FIG. 3B is a cross-sectional view ofthe light guide plate LG, taken along line B1-B2 of FIG. 2A.

In FIG. 3A, the cross-sectional shape of the protrusion part TRVa in thefirst direction X is an isosceles triangle apex of which is above thebase. In FIG. 3A, the apex angle of the isosceles triangle which is thecross-sectional shape of the protrusion part TRVa is set as θ1. The apexangle θ1 is, preferably, between 55 degrees and 60 degrees, inclusive(the apex angle θ1 is in a range of larger than and equal to 55 degrees,and smaller than and equal to 65 degrees). The reason will be explainedlater.

In FIG. 3B, the cross-sectional shape of the protrusion part TRVb in thesecond direction Y is an isosceles triangle apex of which is below thebase. In FIG. 3B, the apex angle of the isosceles triangle which is thecross-sectional shape of the protrusion part TRVb is set as θ2. The baseangle θ2 is, preferably, between 1 degree and 3 degrees, inclusive (thebase angle θ2 is in range of larger than and equal to 1 degree, andsmaller than and equal to 3 degrees). The reason will be explainedlater.

The reason why the apex angle θ1 is preferred to be between 55 degreesand 60 degrees will be explained here. FIGS. 4A, 4B, 5A, 5B, 6A, 6B, 7A,7B, 8A, and 8B illustrate emission angle distribution characteristicswith respect to the apex angle θ1. FIGS. 4A and 4B show a case where theapex angle θ1 of the protrusion part TRVa is 60 degrees, 5A and 5B showa case where the apex angle θ1 is 50 degrees, 6A and 6B show a casewhere the apex angle θ1 is 70 degrees, 7A and 7B show a case where theapex angle θ1 is 80 degrees, and 8A and 8B show a case where the apexangle θ1 is 100 degrees.

FIG. 4A shows an equi-luminosity curve (also called equi-luminance curveor equi-brightness curve) with respect to the emission angles φv and φhof the emission light L of the light emitting device ILD of FIGS. 2A to2C. In FIG. 4A, the horizontal axis indicates the emission angle φh, andthe vertical axis indicates the emission angle φv, and each lineindicates a part of the equi-luminosity. FIG. 4B is a graph indicativeof a relationship between the emission angles φv and φh and theluminosity (also called luminance or brightness) based on FIG. 4A. InFIG. 4B, the horizontal axis indicates the emission angles φv and φh,and the vertical axis indicates the standardized luminosity in which theluminosity of the emission angles φv and φh is standardized. In FIG. 4B,the emission angle φv is plotted in a solid line, and the emission angleφh is plotted in a dotted line.

As in FIG. 4A, if the apex angle θ1 is 60 degrees, the distribution ofluminosity is substantially the same in the emission angles φh (firstdirection X) and φv (second direction Y). That is, the emission light isirradiated evenly in both the first direction X and the second directionY. The state where the light is evenly emitted in both the firstdirection X and the second direction Y can be estimated from the factthat the graphs of the emission angles φv and φh overlap with each otherin many parts.

On the other hand, in FIG. 5A (apex angle θ1=50 degrees), FIG. 6A (apexangle θ1=70 degrees), FIG. 7A (apex angle θ1=80 degrees), and FIG. 8A(apex angle θ1=100 degrees), the equi-luminosity curve is widened in theemission angle φh (first direction X). That is, the light is irradiatedunevenly in the first direction X and the second direction Y.

In FIG. 5B (apex angle θ1=50 degrees), FIG. 6B (apex angle θ1=70degrees), FIG. 7B (apex angle θ1=80 degrees), and FIG. 8B (apex angleθ1=100 degrees), the graphs of the of the emission angles φv and φhoverlap with each other in fewer parts. Thus, in cases where the apexangle θ1 is 50 degrees, 70 degrees, 80 degrees, and 100 degrees, theemission light is uneven in the first direction X and the seconddirection Y.

Using full width at half of the maximum (FWHM) of the graphs of FIGS.4B, 5B, 6B, 7B, and 8B, calculation of a suitable range of the apexangle θ1 will be explained.

Referring to FIG. 4B, a case where the apex angle θ1 is 60 degrees willbe explained. Full width at half of the maximum is derived from thegraph of FIG. 4B, and with full width at half of the maximum, emissionangle φv is −12 degrees and +12 degrees (in range of larger than andequal to −12 degrees, and smaller than and equal to 12 degrees), andemission angle φh is −12 degrees and +12 degrees (in range of largerthan and equal to −12 degrees, and smaller than and equal to 12degrees).

The emission light within the range of full width at half of the maximumof the graph of FIG. 4B, that is, the emission light of emission angleφv between −12 degrees and +12 degrees, inclusive (−12 degrees≤φv≤+12degrees) and emission angle φh between −12 degrees and +12 degrees,inclusive (−12 degrees≤φh≤+12 degrees) is light which can be regarded ascollimated light. Thus, the light emitting device ILD of the presentembodiment should contain as much emission light with emission angles φvand φh within the above range as possible.

In a similar manner as in FIG. 4B, full width at half of the maximum ofeach of the emission angles φv and φh is derived with respect to in FIG.5B (apex angle θ1=50 degrees), FIG. 6B (apex angle θ1=70 degrees), FIG.7B (apex angle θ1=80 degrees), and FIG. 8B (apex angle θ1=100 degrees),and the emission angle φh at full width at half of the maximum isplotted as in FIG. 9 .

Note that, the emission angle φv with full width at half of the maximumis −12 degrees and +12 degrees in each of FIGS. 4B, 5B, 6B, 7B, and 8B,and thus, the evaluation is performed with respect to the emission angleφh alone.

FIG. 9 illustrates a relationship between the emission angle φh and theapex angle θ1. In FIG. 9 , the horizontal axis is apex angle θ1, and thevertical axis is a positive value of emission angle φh at full width athalf of the maximum. The hatched area in FIG. 9 is a range of apex angleθ1 in a case where the positive value of emission angle φh at full widthat half of the maximum is near 12 degrees. As in FIG. 9 , the apex angleθ1 is, preferably, between 55 degrees and 65 degrees, inclusive, andbetween 75 degrees and 100 degrees, inclusive.

Now, noise in the present embodiment will be explained. In the presentembodiment, noise is amount of light emitted at a shallow angle withrespect to the X-Y plan. For example, in FIG. 8B (apex angle θ1=100degrees), in the emission angles φv and φh, emission light can berecognized in the areas between 30 degrees and 90 degrees, inclusive,and between −90 degrees and −30 degrees, inclusive. Greater lightemitted at a shallow angle (noise) means greater emission light wideninghorizontally. The light emitting device ILD emitting collimated lightshould have a lesser noise ratio.

FIG. 10 illustrates a relationship between a noise relative value andapex angle θ1. In FIG. 10 , the horizontal axis is apex angle θ1 and thevertical axis is a noise relative value calculated as follows. That is,in FIG. 8B (apex angle θ1=100 degrees), the luminosity at emission angleφh is 30 degrees is set as 1. With respect to the luminosity, a relativevalue of luminosity at emission angle φh of 30 degrees in FIG. 4B (apexangle θ1=60 degrees), FIG. 5B (apex angle θ1=50 degrees), FIG. 6B (apexangle θ1=70 degrees), FIG. 7B (apex angle θ1=80 degrees), and FIG. 8B(apex angle θ1=100 degrees) is plotted as in FIG. 10 .

The hatched area in FIG. 10 is a range of apex angle θ1 in a case wherethe above-mentioned noise relative value is the minimum value. As inFIG. 10 , the apex angle θ1 is, preferably, between 55 degrees and 65degrees, inclusive (in range of larger than and equal to 55 degrees, andsmaller than and equal to 65 degrees, and between 95 degrees and 100degrees, inclusive (in range of larger than and equal to 95 degrees, andsmaller than and equal to 100 degrees).

Comparing the range between 55 degrees and 65 degrees, inclusive, andthe range between 95 degrees and 100 degrees, inclusive, the rangebetween 55 degrees and 65 degrees has smaller noise relative value thanthe range between 95 degrees and 100 degrees, inclusive.

From the above, it is clearly understood that apex angle θ1 between 55degrees and 65 degrees is suitable for the protrusion part TRVa of thelight guide plate LG of the light emitting device ILD.

Now, the reason why base angle θ2 of the protrusion part TRVb issuitable in a range between 1 degree and 3 degrees, inclusive (in rangeof larger than and equal to 1 degree, and smaller than and equal to 3degrees) will be explained. FIGS. 11A to 11C illustrate changes ofemission angle φv of emission light L based on base angle θ2. FIG. 11Aillustrates emission angle φv and distribution of emission light L in acase where base angle θ2 is small, and FIG. 11B illustrate those in acase where base angle θ2 is great.

As in FIG. 11A, if base angle θ2 is small, emission angle φv is great,and the emission angle distribution is narrow. In other words, emissionlight L is emitted with respect to the main surface LGa of the lightguide plate LG at a shallow angle in a converged manner.

On the other hand, as in FIG. 11B, if base angle θ2 is great, emissionangle φv is small, and the emission angle distribution is wide. In otherwords, emission light L is emitted with respect to the main surface LGaof the light guide plate LG at a deeper angle in a widened manner.

FIG. 11C is a schematic cross-sectional view illustrating the lightguide plate LG, prism sheet PRM, and angle of emission light L. As inFIG. 11C, the emission light L emitted from the light guide plate LG isincident on the prism sheet PRM, reflected inside the protrusion partTRVp of the prism sheet PRM, and emitted above.

In order to obtain the above-mentioned collimated light, the emissionlight L emitted from the prism sheet PRM is desired to be emitted in adirection parallel to the third direction Z.

Here, the emission light L of FIG. 11A has a narrow emission angledistribution, and thus, the amount of light emitted above the prismsheet PRM becomes great. On the other hand, the emission light L of FIG.11B has a wide emission angle distribution, and thus, the light emittedabove from the surface of the prism sheet PRM is widely scattered atvarious angles. That is, the emission light to be taken to a directionparallel to the third direction Z may possibly be insufficient. Thus,the emission angle distribution of the emission light L desired to benarrow. In order to achieve the narrow emission angle distribution,smaller base angle θ2 of the protrusion part TRVb of the light guideplate LG is preferred. In the following description, this will furtherbe explained.

FIGS. 12A, 12B, 13A, and 13B illustrate emission angle distributioncharacteristics with respect to base angle θ2. FIGS. 12A and 12Billustrate a case where base angle θ2 of the protrusion part TRVb is 2degrees, and FIGS. 13A and 13B illustrate a case where the base angle θ2is 5 degrees.

FIGS. 12A and 13A each show an equi-luminosity curve with respect to theemission angles φv and φh as in FIG. 4A. In FIGS. 12A and 13A, thehorizontal axis indicates the emission angle φh, and the vertical axisindicates the emission angle φv, and each line indicates a part of theequi-luminosity.

FIGS. 12B and 13B each illustrate a graph of a relationship between theemission angles φv and φh and the luminosity based on FIGS. 12A and 13A.

Full width at half of the maximum (FWHM) is derived from the graph ofFIG. 12B, and a range of the emission angle φv at full width at half ofthe maximum (corresponding to emission angle distribution) is 24degrees. Full width at half of the maximum (FWHM) is derived from thegraph of FIG. 13B, and a range of the emission angle (φv at full widthat half of the maximum is 38 degrees.

That is, the emission angle distribution is narrower in the graph ofFIG. 12B than the graph of FIG. 13B. Thus, base angle θ2 is better 2degrees than 5 degrees.

Furthermore, evaluation of the emission angle distribution using fullwidth at half of the maximum will be explained with reference to FIG. 14. FIG. 14 illustrates a relationship between emission angle φv and baseangle θ2. In FIG. 14 , the horizontal axis is base angle θ2 ofprotrusion part TRVb, and the vertical axis is a range of emission angleφv at full width at half of the maximum.

As in FIG. 14 , when base angle θ2 increases, the range of emissionangle φv increases accordingly. That is, if θ2 is small, the emissionangle distribution is narrow. However, since base angle θ2 cannot be 0degrees, the suitable range of base angle θ2 is 1 degree≤θ2≤3 degrees(angle θ2 is in a range of larger than and equal to 1 degree, andsmaller than and equal to 3 degrees). If the base angle is below 1degree, the efficiency of emission of light from the light guide plateLG is decreased, and especially, if the base angle is 0 degrees, lightemission from the light guide plate LG cannot be performed.

From the above-described embodiment, it is clearly understood that baseangle θ2 satisfying 1 degree≤θ2≤3 degrees is suitable in the protrusionpart TRVb of the light guide plate LG of the light emitting device ILD.

The light emitting device ILD of the present embodiment can emitcollimated light as described above. When a light collection device islaminated on the light emitting device ILD, an illumination device whichcan control the light emission direction can be achieved. Hereinafter,the illumination device of the present embodiment will be explained.

FIG. 15 illustrates an example of the structure of an illuminationdevice ILM. The illumination device ILM of FIG. 15 includes theabove-described light emitting device ILD, and a light collection deviceLSM overlapping the light emitting device ILD in the third direction Z.

The illumination device ILM includes a controller CT. The controller CTincludes controllers ICT and LCT. The controller ICT is to control thelight emitting device ILD, and the controller LCT is to control thelight collection device LSM. The controller ICT controls current to thelight source element LS1 of, for example, FIG. 1 . The controller LCTwill be described later.

FIG. 16 is a schematic cross-sectional view of the light collectiondevice LSM. The light collection device LSM includes a first substrateSUB1, second substrate SUB2, liquid crystal layer LC with a plurality ofliquid crystal molecules, first controller electrode ELE1, and secondcontroller electrode ELE2. In the example depicted, the first controllerelectrode ELE1 is provided with the first substrate SUB1, and the secondcontroller electrode ELE2 is provided with the second substrate SUB2.However, the first controller electrode ELE1 and the second controllerelectrode ELE2 may be disposed on the same substrate, that is, may bedisposed on the first substrate SUB1 or the second substrate SUB2.

The first substrate SUB1 includes a transmissive base BA1, firstcontroller electrode ELE1, alignment film ALA1, and power supplied lineSPL. The first controller electrode ELE1 is disposed between the baseBA1 and the liquid crystal layer LC. The first controller electrodesELE1 are arranged in the first direction X at intervals. In thisexample, the width of the first controller electrode ELE1 in the firstdirection X is equal to or less than a gap between adjacent firstcontroller electrodes ELE1 in the first direction X. The alignment filmALA1 covers the first controller electrode ELE1 and contacts the liquidcrystal layer LC. The power supply line SPL is positioned in anon-active area NA which is outside of an active area AA.

The second substrate SUB2 includes a transmissive base BA2, secondcontroller electrode ELE2, and alignment film ALA2. The secondcontroller electrode ELE2 is disposed between the base BA2 and theliquid crystal layer LC. The second controller electrode ELE2 is asingle flat-plate electrode disposed substantially in the entire surfaceof the active area AA and extending to the non-active area NA. Thesecond controller electrode ELE2 is, in the active area AA, opposed tothe first controller electrode ELE1 via the liquid crystal layer LC. Thesecond controller electrode ELE2 is opposed to the power supply line SPLin the non-active area NA. The second controller electrode ELE2 isopposed to the power supply line SPL in the non-active area NA. Thealignment film ALA2 covers the second controller electrode ELE2, andcontacts the liquid crystal layer LC.

The bases BA1 and BA2 are, for example, a glass substrate or a resinsubstrate. The first controller electrode ELE1 and the second controllerelectrode ELE2 are formed of a transparent conductive material such asindium tin oxide (ITO) or indium zinc oxide (IZO). The alignment filmsALA1 and ALA2 are, for example, a horizontal alignment film, and alignedin the first direction X.

The first substrate SUB1 and the second substrate SUB2 are adhered toeach other in the non-active area NA with a sealant SAL. The sealant SALincludes conductive material CDP. The conductive material CDP isinterposed between the power supply line SPL and the second controllerelectrode ELE2, to electrically connect the power supply line SPL andthe second controller electrode ELE2.

The liquid crystal layer LC is held between the first substrate SUB1 andthe second substrate SUB2. The liquid crystal layer LC is formed of, forexample, liquid crystal material with positive dielectric anisotropy.The first controller electrode ELE1 and the second controller electrodeELE2 change the alignment direction of the liquid crystal molecules LCMin the liquid crystal layer LC by applying a voltage to the liquidcrystal layer LC. When the alignment direction of the liquid crystalmolecules LCM is changed, a liquid crystal lens LNS is formed in theliquid crystal layer LC.

The controller LCT controls the voltage to be applied to the liquidcrystal layer LC. The controller LCT controls the voltage supplied toeach of the first controller electrode ELE1 and the second controllerelectrode ELE2 in order to control a degree of the change of thealignment direction of the liquid crystal molecules LCM in the liquidcrystal layer LC. Furthermore, the controller LCT controls the voltagesupplied to each first controller electrode ELE1 in order to control aradius, focal length, formation position, and the like of the liquidcrystal lens LNS.

FIG. 17 is a plan view of a shape of the first controller electrode ELE1of the light collection device LSM. The first controller electrode ELE1of FIG. 17 includes multiple arcuate electrodes ELE1 a (only the centerof which is circular) and draw electrodes WL. Each arcuate electrodeELE1 a is connected to the controller ICT through the draw electrode WL.

As described above, by changing the voltage supplied from the controllerLCT to the first controller electrode ELE1, radius, focal distance,formation position, and the like of the liquid crystal lens LNS can bechanged.

According to the present embodiment, a light emitting device which canemit collimated light, and an illumination device including the lightemitting device can be obtained. The illumination device can emit lightwith directivity, and thus, emission direction can be specificallycontrolled.

EXAMPLE

FIGS. 18A and 18B illustrate a light emitting device of the example. Thelight emitting device ILD of FIG. 18A is structured the same as that ofFIG. 2A, and thus, detailed description of FIGS. 2A to 2C is appliedhere. In the light emitting device ILD of FIG. 18A, the light guideplate LG is formed of a polycarbonate material refractive index of whichis 1.58. The light guide plate has a length W of 90 mm in the firstdirection X, length H of 90 mm in the second direction Y, and length(thickness) T of 2.0 mm in the third direction Z.

The protrusion part TRVa of the light guide plate LG has a triangularprism shape extending in the second direction Y. The cross-sectionalshape of the protrusion part TRVa in the first direction X is anisosceles triangle with apex angle θ1 of 60 degrees.

The protrusion part TRVb of the light guide plate LG has a triangularprism shape extending in the first direction X. The cross-sectionalshape of the protrusion part TRVb of the light guide plate LG in thesecond direction Y is an isosceles triangle with base angle θ2 of 2degrees (apex angle of 176 degrees).

FIG. 18B is a cross-sectional view of the prism sheet PRM of FIG. 18A,taken along line C1-C2. The prism sheet PRM is formed of an acrylicmaterial refractive index of which is 1.52. On the prism sheet PRM, asdescribed above, triangular prism shaped protrusion parts TRVp extendingin the first direction X are disposed. The cross-sectional shape of theprotrusion part TRVp in the second direction Y is an isosceles triangleapex of which is positioned below the base. The apex angle of theisosceles triangle which is the cross-sectional shape of the protrusionpart TRVp is an apex angle θ3. In FIGS. 18A and 18B, apex angle θ3 is 68degrees.

The reflection sheet REF of FIG. 18A is formed of a silver depositedspecular reflection material. The light source element LS1 is lightemitting diode (LED).

The graph of the relationship between emission angles φv and φh andluminosity with respect to emission light from the light emitting deviceILD of FIGS. 18A and 18B is shown in FIG. 4B. Since the description ofFIG. 4B has been explained above, the detailed description thereof isnot repeated here. In the present embodiment, the light emitting devicewhich can emit collimated light can be achieved as above.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A light emitting device comprising: a light guideplate having a first main surface, a second main surface, a first sidesurface, a second side surface opposite to the first side surface, athird side surface adjacent to the first side surface and the secondside surface and a fourth side surface opposite to the third sidesurface; and a light source element disposed on the first side surfaceof the light guide plate, wherein the light guide plate has a firstprotrusion part on the first main surface and a second protrusion parton the second main surface, a plurality of the first protrusion partsare arranged along a first direction and extended along a seconddirection which crosses the first direction, the first protrusion parthas a first ridge extending from the first side surface to the secondside surface, a plurality of the second protrusion parts are arrangedalong the second direction and extended along the first direction, thesecond protrusion part has a second ridge extending from the third sidesurface to the fourth side surface, a cross-sectional shape of each ofthe first protrusion parts has an apex angle between 55 and 65 degrees,inclusive, a cross-sectional shape of each of the second protrusionparts has a base angle between 1 and 3 degrees, inclusive, an emissionsurface of the light source element is disposed in the second direction,and a reflection sheet disposes to be opposed to the second main surfaceof the light guide plate.
 2. The light emitting device according toclaim 1, wherein a prism sheet disposes to be opposed to the first mainsurface.
 3. The light emitting device according to claim 2, wherein theprism sheet includes a plurality of protrusion parts on the surfaceopposed to the light guide plate, which extend along the first directionand are arranged in the second direction, and each of the protrusionparts of the prism sheet has a cross-sectional shape along the seconddirection as an isosceles triangle in which the apex angle is positionedbelow the base.
 4. The light emitting device according to claim 1,wherein the light source element includes a first light source elementand a second source element, the first light source element is disposedon the first side surface, and the second light source element isdisposed on the second side surface.
 5. An illumination devicecomprising: the light emitting device according to claim 1; and a lightcollection device overlapping the light emitting device.
 6. Theillumination device according to claim 5, wherein the light collectiondevice includes a liquid crystal layer in which a liquid crystal lens isformed.